From 92488d46a0deca6d031d07852c3b79214280ab6d Mon Sep 17 00:00:00 2001
From: Michael Vrable <mvrable@cs.ucsd.edu>
Date: Sat, 30 May 2009 23:19:10 -0700
Subject: [PATCH] Implement metadata caching for S3 backend.

Amazon S3 will return some limited object metadata when a list operation is
performed.  This is significantly cheaper than fetching the information for
objects one at a time.  In the S3 backend, implement a scan() method that
will list all objects and cache the metadata, then return cached results
when stat() is called.
---
 python/cumulus/__init__.py       |  3 +++
 python/cumulus/store/__init__.py | 11 +++++++++++
 python/cumulus/store/s3.py       | 14 +++++++++++++-
 3 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/python/cumulus/__init__.py b/python/cumulus/__init__.py
index 46a7b5f..5418d3c 100644
--- a/python/cumulus/__init__.py
+++ b/python/cumulus/__init__.py
@@ -119,6 +119,9 @@ class LowlevelDataStore:
                 return (t, filename)
         return (None, filename)
 
+    def scan(self):
+        self.store.scan()
+
     def lowlevel_open(self, filename):
         """Return a file-like object for reading data from the given file."""
 
diff --git a/python/cumulus/store/__init__.py b/python/cumulus/store/__init__.py
index 7c43b69..35de0ee 100644
--- a/python/cumulus/store/__init__.py
+++ b/python/cumulus/store/__init__.py
@@ -26,6 +26,17 @@ class Store:
     def delete(self, type, name):
         raise NotImplementedException
 
+    def stat(self, type, name):
+        raise NotImplementedException
+
+    def scan(self):
+        """Cache file information stored in this backend.
+
+        This might make subsequent list or stat calls more efficient, but this
+        function is intended purely as a performance optimization."""
+
+        pass
+
 def open(url):
     (scheme, netloc, path, params, query, fragment) \
         = urlparse.urlparse(url)
diff --git a/python/cumulus/store/s3.py b/python/cumulus/store/s3.py
index 1e7257a..63efa17 100644
--- a/python/cumulus/store/s3.py
+++ b/python/cumulus/store/s3.py
@@ -11,12 +11,19 @@ class S3Store(cumulus.store.Store):
         self.bucket = self.conn.create_bucket(bucket)
         while prefix.endswith("/"): prefix = prefix[:-1]
         self.prefix = prefix
+        self.scan_cache = {}
 
     def _get_key(self, type, name):
         k = Key(self.bucket)
         k.key = "%s/%s/%s" % (self.prefix, type, name)
         return k
 
+    def scan(self):
+        prefix = "%s/" % (self.prefix,)
+        for i in self.bucket.list(prefix):
+            assert i.key.startswith(prefix)
+            self.scan_cache[i.key] = i
+
     def list(self, type):
         prefix = "%s/%s/" % (self.prefix, type)
         for i in self.bucket.list(prefix):
@@ -38,7 +45,12 @@ class S3Store(cumulus.store.Store):
         self.bucket.delete_key("%s/%s/%s" % (self.prefix, type, name))
 
     def stat(self, type, name):
-        k = self.bucket.get_key("%s/%s/%s" % (self.prefix, type, name))
+        path = "%s/%s/%s" % (self.prefix, type, name)
+        if path in self.scan_cache:
+            k = self.scan_cache[path]
+        else:
+            k = self.bucket.get_key(path)
         if k is None:
             raise cumulus.store.NotFoundError
+
         return {'size': int(k.size)}
-- 
2.20.1